The purpose of this module is to demonstrate how to use spatial layers from a Spatial Data Engine (SDE). QGIS supports data provided with PostGIS/PostgreSQL, which is an open source Spatial Data Engine (or Database Management System) with the ability to store, manipulate and serve spatial GIS data. Oracle Spatial and ArcSDE are the commercial counterparts of the PostGIS.
Figure 1.
The SDE provides centralized access to spatial data, which can be beneficial for large organizations or projects with a significant number of GIS users. The SDE is a layer between a GIS application and the database management system. The general framework for QGIS and PostGIS is presented in Figure 1. In addition to local spatial data (stored on your hard drive), you can use spatial layers from PostGIS. This approach extends the functionality of QGIS and allows one to:
join attribute tables to spatial layers
use subsets of spatial layers instead of the whole layer
perform complex operations on database/attribute tables, etc.
In the next sections, we will demonstrate how to use/incorporate spatial layers from the SDE. We will create a map of residential development in Amherst, MA and overlay this map with a map of Western Massachusetts. We will utilize a landuse layer and the MA towns layer from the FossGIS spatial server. The trick is in that we will use only a SUBSET of those layers. Okay, lets start.
Please start QGIS and create a new project.